Language Reference
TWNDOW
The predened windows simulate passband shapes that represent a give-and-take between amplitude uncertainty, sensitivity, and wavelength resolution. They also minimize side eects caused by the non-continuous, nite nature of the discrete Fourier transform. One side eect is the appearance of aliasing. This is handled by rapid sampling and signal ltering. Another side eect is spurious responses caused by sampling the measurement range for a nite period. This is minimized by weighting the sampled data, but this reduces the resolution of real signals. The compromise of how much to reduce side lobes at the expense of resolution is the purpose of the window choices.
The uniform-window algorithm has the least wavelength uncertainty and greatest amplitude uncertainty. Worst-case accuracy uncertainty is 03.9 dB and its 3 dB resolution bandwidth is 60% of the Hanning bandwidth.
The uniform window does not contain time-domain weighting. Thus, the amplitude data is unchanged. Use the uniform window when transforming noise signals or transients that decay within one sweep-time period. The uniform window also yields the best wavelength resolution, but also produces the highest side lobes for periodic signals.
The Hanning window is a traditional passband window found in most real-time spectrum analyzers. The Hanning window oers a compromise between the at-top and uniform windows. Its amplitude uncertainty is
01.5 dB and its 3-dB bandwidth is 40% of the at-top bandwidth. Use the Hanning window when transforming periodic or random data.
The at-top window has the greatest wavelength uncertainty of the windows, but it has outstanding side-lobe suppression and amplitude atness. Use the at-top window to transform periodic signals.
The Hamming window has a bandwidth somewhere between the Hanning and at-top windows, with more uniform side-lobe suppression than the Hanning window, but less suppression than either Hanning or at-top for signals farther out of the passbands.
See Also FFT, TWNDOW